In the production of chips from wood raw material, chippers of the above described type are used. Such chippers can be of the type that is used in order to chip, from the entire wood raw material, chips for production of paper pulp or production of boards, but can also be “reducers” which are used for forming blocks of round logs and which have on the one hand chipper knives for chipping the material that is to be removed from the logs into chips, and on the other cleaning knives to provide fine working of the block surfaces.
Chippers are operated under highly varying conditions where the hardness of the wood can vary to a great extent depending on type of tree, temperature with the respect to frozen or unfrozen wood, knottiness, fine grain and the like. The hardness and nature of the wood is important to the cutting edge angle which the chipper knives, and the cleaning knives for that matter, should have for optimum operational economy.
Furthermore, there are many different types, makes and sizes of chippers on the market, which may require different chipping geometries, that is geometry of that part of the chipper knife that is directly involved in chipping, that is the cutting edge and the area on both sides next to the cutting edge. The term cutting geometry relates to, inter alia, the cutting edge angle, the angle of the edge-forming surface on the wood side, that is the side oriented toward the pieces of wood arriving at the chipper knives, relative to the direction of motion of the chipper knife and the angle of the edgeforming surface on the chip side, that is the side of the chipper knife where the chips are separated, relative to the direction of motion of the chipper knife. In some cases it may be desirable to change the chipping geometry of the chipper knife in order to control, for instance, the chip size or the chipping power.
Summing up, this means that each type and size of chipper knife has to be manufactured and kept in stock in many variants with different cutting edge angles, different angles of the edge-forming surface on the wood side and/or different angles of the edge-forming surface on the chip side. This results in high costs of manufacture and stock-keeping of the chipper knives.